1. Field of the Invention
The invention relates in general to a display, a pixel circuit and a driving method thereof, and more particularly to a lighting emitting display, a pixel circuit of a light emitting diode (LED) and a driving method thereof.
2. Description of the Related Art
An organic light emitting display has no limitation to the viewing angle, has the low power consumption, may be easily manufactured and has the high response speed, so the organic light emitting display has become the next generation of the display technology. In the organic light emitting display, an organic film is evaporated between a transparent anode and a metal cathode, and electrons and holes are introduced between the transparent anode and the metal cathode to combine together between the organic films so that the energy can be converted into visible light. In addition, different organic materials may be used to output the light with different colors so that the requirement of the full-color display may be satisfied.
In a pixel circuit of the organic light emitting display, the luminance outputted from the pixel may be different from an expected one due to the threshold voltage variation of each MOS transistor and the influence of the mobility shift. Thus, it is very important to compensate the pixel structure or the driving method in the above-mentioned state. FIG. 1 (PriorArt) shows a conventional pixel circuit 100 capable of compensating a mobility shift. Referring to FIG. 1, the pixel circuit 100 includes transistors K1 to K5, a capacitor Cst and an organic light-emitting diode O1. In the pixel circuit 100, the transistors K2 and K4 form a current mirror to control the current flowing through the organic light-emitting diode O1. However, the dismatch between the transistors K2 and K4 may make the behavior of the pixel be worse than the expected behavior.
FIG. 2 (Prior Art) shows another conventional pixel circuit 200 capable of compensating the mobility shift. Referring to FIG. 2, the pixel circuit 200 includes transistors T1 to T7, a capacitor C and an organic light-emitting diode OLED. Compared with the pixel circuit of FIG. 1, the problem of dismatch between the transistors K2 and K4 can be overcome, but the number of transistors in the pixel circuit 200 is greater than that in the pixel circuit 100. So, the aperture ratio is influenced and the cost is increased.